package org.apache.solr.search;

import org.apache.lucene.search.*;
import org.apache.lucene.index.IndexReader;
import org.apache.solr.search.function.ValueSource;
import org.apache.solr.common.SolrException;

import java.io.IOException;
import java.util.Set;
import java.util.Map;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * A query that wraps a filter and simply returns a constant score equal to the
 * query boost for every document in the filter. This Solr extension also
 * supports weighting of a SolrFilter.
 * 
 * Experimental and subject to change.
 */
public class SolrConstantScoreQuery extends ConstantScoreQuery implements
		ExtendedQuery {
	boolean cache = true; // cache by default
	int cost;

	public SolrConstantScoreQuery(Filter filter) {
		super(filter);
	}

	/** Returns the encapsulated filter */
	@Override
	public Filter getFilter() {
		return filter;
	}

	public void setCache(boolean cache) {
		this.cache = cache;
	}

	public boolean getCache() {
		return cache;
	}

	public void setCacheSep(boolean cacheSep) {
	}

	public boolean getCacheSep() {
		return false;
	}

	public void setCost(int cost) {
		this.cost = cost;
	}

	public int getCost() {
		return cost;
	}

	@Override
	public Query rewrite(IndexReader reader) throws IOException {
		return this;
	}

	@Override
	public void extractTerms(Set terms) {
		// OK to not add any terms when used for MultiSearcher,
		// but may not be OK for highlighting
	}

	protected class ConstantWeight extends Weight {
		private Similarity similarity;
		private float queryNorm;
		private float queryWeight;
		private Map context;

		public ConstantWeight(Searcher searcher) throws IOException {
			this.similarity = getSimilarity(searcher);
			this.context = ValueSource.newContext();
			if (filter instanceof SolrFilter)
				((SolrFilter) filter).createWeight(context, searcher);
		}

		@Override
		public Query getQuery() {
			return SolrConstantScoreQuery.this;
		}

		@Override
		public float getValue() {
			return queryWeight;
		}

		@Override
		public float sumOfSquaredWeights() throws IOException {
			queryWeight = getBoost();
			return queryWeight * queryWeight;
		}

		@Override
		public void normalize(float norm) {
			this.queryNorm = norm;
			queryWeight *= this.queryNorm;
		}

		@Override
		public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder,
				boolean topScorer) throws IOException {
			return new ConstantScorer(similarity, reader, this);
		}

		@Override
		public Explanation explain(IndexReader reader, int doc)
				throws IOException {

			ConstantScorer cs = new ConstantScorer(similarity, reader, this);
			boolean exists = cs.docIdSetIterator.advance(doc) == doc;

			ComplexExplanation result = new ComplexExplanation();

			if (exists) {
				result.setDescription("ConstantScoreQuery(" + filter
						+ "), product of:");
				result.setValue(queryWeight);
				result.setMatch(Boolean.TRUE);
				result.addDetail(new Explanation(getBoost(), "boost"));
				result.addDetail(new Explanation(queryNorm, "queryNorm"));
			} else {
				result.setDescription("ConstantScoreQuery(" + filter
						+ ") doesn't match id " + doc);
				result.setValue(0);
				result.setMatch(Boolean.FALSE);
			}
			return result;
		}
	}

	protected class ConstantScorer extends Scorer {
		final DocIdSetIterator docIdSetIterator;
		final float theScore;
		int doc = -1;

		public ConstantScorer(Similarity similarity, IndexReader reader,
				ConstantWeight w) throws IOException {
			super(similarity, w);
			theScore = w.getValue();
			DocIdSet docIdSet = filter instanceof SolrFilter ? ((SolrFilter) filter)
					.getDocIdSet(w.context, reader) : filter
					.getDocIdSet(reader);
			if (docIdSet == null) {
				docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
			} else {
				DocIdSetIterator iter = docIdSet.iterator();
				if (iter == null) {
					docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
				} else {
					docIdSetIterator = iter;
				}
			}
		}

		@Override
		public int nextDoc() throws IOException {
			return docIdSetIterator.nextDoc();
		}

		@Override
		public int docID() {
			return docIdSetIterator.docID();
		}

		@Override
		public float score() throws IOException {
			return theScore;
		}

		@Override
		public int advance(int target) throws IOException {
			return docIdSetIterator.advance(target);
		}

		public Explanation explain(int doc) throws IOException {
			throw new UnsupportedOperationException();
		}
	}

	@Override
	public Weight createWeight(Searcher searcher) {
		try {
			return new SolrConstantScoreQuery.ConstantWeight(searcher);
		} catch (IOException e) {
			// TODO: remove this if ConstantScoreQuery.createWeight adds
			// IOException
			throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, e);
		}
	}

	/** Prints a user-readable version of this query. */
	@Override
	public String toString(String field) {
		return "ConstantScore(" + filter.toString()
				+ (getBoost() == 1.0 ? ")" : "^" + getBoost());
	}

	/** Returns true if <code>o</code> is equal to this. */
	@Override
	public boolean equals(Object o) {
		if (this == o)
			return true;
		if (!(o instanceof SolrConstantScoreQuery))
			return false;
		SolrConstantScoreQuery other = (SolrConstantScoreQuery) o;
		return this.getBoost() == other.getBoost()
				&& filter.equals(other.filter);
	}

	/** Returns a hash code value for this object. */
	@Override
	public int hashCode() {
		// Simple add is OK since no existing filter hashcode has a float
		// component.
		return filter.hashCode() + Float.floatToIntBits(getBoost());
	}

}
